A simple way to transform a DC voltage is to use a voltage divider circuit. However, voltage dividers are inefficient since a portion of the input voltage is discharged as heat. The excess heat can affect the operating characteristics of other circuit components, even causing other components to default. In addition, there is no method of regulating the output voltage of the voltage divider circuit, since the output voltage varies with the input voltage.
A Buck converter, on the other hand, can be remarkably efficient and self-regulating, making it useful for tasks such as converting a typical 12-24V battery voltage in a laptop down to a few volts required to power a processor, for example. A Buck converter operates as a switched-mode power supply that uses two switches (typically a transistor and a diode), an inductor and a load capacitor to step-down a DC source voltage according to a specified duty cycle.
In operation, the switches control the connection of the inductor to a source voltage. The switches electrically couple the inductor to the source voltage during a charging portion of a clocking period, thereby storing energy in the inductor. The switches electrically decouple the inductor from the source voltage during a discharging portion of the clocking period, enabling the inductor to discharge stored electromagnetic energy into a load. The duty cycle is the ratio of the charging time period to the discharging time period, which for an ideal converter, is equivalent to the ratio of the output voltage measured across the load to the source voltage.
Some Buck converters utilize feedback control loops to control operation of the switches and stabilize the output voltage, and hence, stabilize the duty cycle. These feedback control loops typically use clocking pulses of fixed width to control the switches. However, using fixed width clocking pulses places operational constraints on converter clocking frequencies and may cause voltage output instabilities in the form of sub-harmonic circuit oscillations.